1. Field of the Invention
The present invention relates to a process for producing optical elements with a gradient structure. The optical elements are suitable in particular for holographic applications, planar gradient index lenses in imaging optics, head-up displays, head-down displays, optical waveguides, especially for optical communications and transmission technology, and optical data storage media.
2. Discussion of Background Information
U.S. Pat. Nos. 5,552,261 and 5,529,473 disclose utilizing the diffusion of monomers whose refractive index is greater or less than that of a surrounding liquid matrix in order to generate a refractive index gradient. This effect, which in the case of photopolymers is known as the Colburn-Haines effect, may lead, following subsequent polymerization, to a product featuring refractive index gradients. In the case of organic monomers, however, only a slight change in refractive index and hence an inadequate refractive index gradient is possible. Additionally, long process times are necessary, and there are high scattering losses.
WO 97/38333 describes optical components with a gradient structure or refractive index gradient, in which the gradient is formed by directed diffusion of nanoscale particles in a liquid matrix phase as a result of a potential difference. The gradient formed is subsequently fixed by polymerization/curing of the matrix. It is possible by this means to generate a pronounced refractive index gradient, but the process sequence for producing defined optical elements is often very complex.
It would be desirable to have available a simple, universally applicable and cost-effective process for producing optical elements with a gradient structure, in particular with a refractive index gradient.